I was able to assign with one character but not another. Will post to bug report when I get home.
Could you tell me if the character that successfully received the troops had a unit in group 0 (the blank group I believe). Here is what I see when I attempt to assign and fail, the receiving character generates a message that the troops are assigned to group 0. Previously this could never happen, assigned troops always went to a defined group starting with a, I believe the code picked the first group that did not already have a soldier assigned. With Tom's change to allows group actions to be performed on the blank group, it would appear that troops can be transferred into that group.
The other thing I have noticed, I cannot change the group designation of any of my troops.